Without adequate lubrication, industrial tools and machines such as compressors can be seriously damaged or destroyed. In many applications, a pump pressurizes a lubricant which is then distributed to multiple lubrication points using a device referred to as a “divider block” or “divider valve.” In a divider block, the pressurized lubricant causes a set of pistons to move back and force in within piston bores, the moving pistons opening and closing internal fluids channels, so that a known volume of fluid is distributed to multiple outlet channels, once for every cycle of the group of cylinders. Because the pistons in the divider block are powered by the pressure of the fluid being distributed, no additional source of power is necessary to operate the divider block.
Divider blocks have been used to distribute lubricating oil to compressors for about fifty years, and they have changed little since their introduction. Because of the relative simplicity of divider blocks, users have been confident that divider blocks accurately distribute a fixed quantity of lubricant or other fluid to each outlet during each cycle of the divider block. When lubricated equipment fails, a technician will typically check to see that the divider block is cycling, and if it is, then assume that the equipment failure was not caused by a lack of lubrication. It has been observed that pistons within divider blocks occasionally wear out, but that is typically attributed to the large number of cycles and the close fit of the piston within the cylinder.
FIG. 1 shows the construction of a typical prior art divider block 100. Divider block 100 is built from multiple sections, including a base plate 102 and multiple divider block sections 104 mounted on the base plate 102. Each divider block section 104 includes an internal piston (not shown) within a bore (not shown). The base plate 102 is comprised of multiple sections, including an inlet section 108 connected to a pressurized fluid source (not shown), one or more intermediate base plate sections 110, and an end section 112. A divider block section 104 is mounted on each intermediate base plate section 110.
The inlet section 108, end section 112, and intermediate base plate sections 110 include internal channels (not shown) for fluid movement and holes for moving fluid between adjacent sections of base plate 102. Each intermediate base plate section 110 also includes an outlet (not shown) for dispensing the fluid, and holes for moving fluid in and out of the corresponding divider block sections 104.
Divider block sections 104 are typically available in a variety of bore sizes. Sizes are indicated as thousandth of a cubic inch displacement, such as sizes 6, 9, 12, 18, 24, and 30. In some divider blocks, inlet section 108 and/or the end section 112 are formed from a block that also includes an intermediate base plate. Additional intermediate base plate sections 110 can be inserted, along with corresponding divider block sections 102, to provide as many fluid outlets as necessary.
As shown in FIG. 1, each divider block section 104 is typically bolted to its corresponding intermediate base plate 110 using two bolts 120. The bolt holes are not positioned along a center line of the divider block section 104, because centered bolt holes would interfere with internal fluid passages. The bolt heads are typically recessed in a counterbore in the divider block section 104. The end section 112, inlet section 108, and intermediate base plates 110 are also bolted together using three bolts with threads on each end and a nut to tighten the manifold pieces together. Another design to bolt the inlet, intermediate and end section base plates 110 together uses hollow bolts with threads on the inside and outside, and solid bolts are inserted into the hollow bolts to manifold the intermediate and end sections together. The insert is threaded into one intermediate base plate 110, and then a bolt (not shown) through the next intermediate base plate 110 is threaded into the internal threads of the insert. This arrangement allows any number of intermediate base plates to be connected together.
FIG. 2 shows a base plate 102 including three intermediate base plate sections 110 without divider block sections 104. FIG. 2 shows holes 210 though which fluid passes between the base plate sections 110 and divider block sections 104, and threaded holes 212 for receiving mounting bolts 120 (FIG. 1). FIG. 3 shows a side view of a base plate 102 of FIG. 1, showing the three intermediate base sections 110, the input section 108, and the end section 112. Each intermediate base section 110 includes an outlet port 312. Outlet port 312 typically includes internal pipe threads so that an outlet pipe can screw directly into output port 312.
FIG. 4 shows a cross-section of a divider block section 104. Within a piston bore 400 is positioned a piston 402. Piston 402 typically includes two sections 404 of reduced diameter separating three sections 406 having a diameter that just fits within bore 400. Fluid can readily pass around sections 404, whereas fluid does not readily pass around sections 406, thereby allowing fluid pressure to move piston 402. The piston clearance within a piston bore is typically designed to be about 0.0003 inches (three ten-thousandths of an inch). A plug 408 is shown at one end of the bore 400. Bolt holes 410 are used for passage of bolts 120 that connect divider block section 402 to an intermediate base section 110, and indicator ports 412 are used to allow oil to either pass through the port from passage 414 or to be exposed in the port for trouble shooting purposes. FIG. 5 shows a front view of the divider block section 104 of FIG. 1. FIG. 5 shows bolt holes 410 and plugs 504 in indicator ports 412. FIG. 6 shows an end view of a divider block section 110 without plug 408, so piston 402 is visible in piston bore 400. This end view also shows the thin wall of metal above the piston, which is associated with failure of the piston to dispense accurate volumes of fluid in high pressure applications.
Over the years, industry has been experiencing unexplained equipment failures or reduced equipment life. Examination of the divider block used to lubricate the failed equipment often shows that the divider block is cycling properly, thereby leaving the cause of the failure a mystery.